custom relayer

circuits/withdraw.circom

@@ -31,6 +31,7 @@ template Withdraw(levels, rounds) {
     signal input root;
     signal input nullifierHash;
     signal input receiver; // not taking part in any computations
+    signal input relayer; // not taking part in any computations
     signal input fee; // not taking part in any computations
     signal private input nullifier;
     signal private input secret;
@@ -56,8 +57,10 @@ template Withdraw(levels, rounds) {
     // Squares are used to prevent optimizer from removing those constraints
     signal receiverSquare;
     signal feeSquare;
+    signal relayerSquare;
     receiverSquare <== receiver * receiver;
     feeSquare <== fee * fee;
+    relayerSquare <== relayer * relayer;
 }
 
 component main = Withdraw(16, 220);

cli.js

@@ -75,6 +75,7 @@ async function withdraw(note, receiver) {
     root: root,
     nullifierHash,
     receiver: bigInt(receiver),
+    relayer: bigInt(0),
     fee: bigInt(0),
 
     // private

contracts/ERC20Mixer.sol

@@ -36,12 +36,12 @@ contract ERC20Mixer is Mixer {
     safeErc20TransferFrom(msg.sender, address(this), mixDenomination);
   }
 
-  function _processWithdraw(address payable _receiver, uint256 _fee) internal {
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee) internal {
     _receiver.transfer(userEther);
 
     safeErc20Transfer(_receiver, mixDenomination - _fee);
     if (_fee > 0) {
-      safeErc20Transfer(operator, _fee);
+      safeErc20Transfer(_relayer, _fee);
     }
   }
 

contracts/ETHMixer.sol

@@ -23,10 +23,10 @@ contract ETHMixer is Mixer {
   ) Mixer(_verifier, _mixDenomination, _merkleTreeHeight, _emptyElement, _operator) public {
   }
 
-  function _processWithdraw(address payable _receiver, uint256 _fee) internal {
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee) internal {
     _receiver.transfer(mixDenomination - _fee);
     if (_fee > 0) {
-      operator.transfer(_fee);
+      _relayer.transfer(_fee);
     }
   }
 

contracts/Mixer.sol

@@ -14,7 +14,7 @@ pragma solidity ^0.5.8;
 import "./MerkleTreeWithHistory.sol";
 
 contract IVerifier {
-  function verifyProof(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) public returns(bool);
+  function verifyProof(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[5] memory input) public returns(bool);
 }
 
 contract Mixer is MerkleTreeWithHistory {
@@ -29,7 +29,7 @@ contract Mixer is MerkleTreeWithHistory {
   uint256 public mixDenomination;
 
   event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
-  event Withdraw(address to, uint256 nullifierHash, uint256 fee);
+  event Withdraw(address to, uint256 nullifierHash, address relayer, uint256 fee);
 
   /**
     @dev The constructor
@@ -75,19 +75,20 @@ contract Mixer is MerkleTreeWithHistory {
       - the receiver of funds
       - optional fee that goes to the transaction sender (usually a relay)
   */
-  function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) public {
+  function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[5] memory input) public {
     uint256 root = input[0];
     uint256 nullifierHash = input[1];
     address payable receiver = address(input[2]);
-    uint256 fee = input[3];
+    address payable relayer = address(input[3]);
+    uint256 fee = input[4];
     require(fee < mixDenomination, "Fee exceeds transfer value");
     require(!nullifierHashes[nullifierHash], "The note has been already spent");
 
     require(isKnownRoot(root), "Cannot find your merkle root"); // Make sure to use a recent one
     require(verifier.verifyProof(a, b, c, input), "Invalid withdraw proof");
     nullifierHashes[nullifierHash] = true;
-    _processWithdraw(receiver, fee);
-    emit Withdraw(receiver, nullifierHash, fee);
+    _processWithdraw(receiver, relayer, fee);
+    emit Withdraw(receiver, nullifierHash, relayer, fee);
   }
 
   function toggleDeposits() external {
@@ -105,6 +106,6 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   function _processDeposit() internal {}
-  function _processWithdraw(address payable _receiver, uint256 _fee) internal {}
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee) internal {}
 
 }

test/ERC20Mixer.test.js

@@ -127,6 +127,7 @@ contract('ERC20Mixer', accounts => {
         // public
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        relayer: operator,
         receiver,
         fee,
 
@@ -167,6 +168,7 @@ contract('ERC20Mixer', accounts => {
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.relayer.should.be.eq.BN(operator)
       logs[0].args.fee.should.be.eq.BN(feeBN)
       isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(true)
@@ -207,6 +209,7 @@ contract('ERC20Mixer', accounts => {
         // public
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        relayer: operator,
         receiver,
         fee,
 
@@ -249,6 +252,7 @@ contract('ERC20Mixer', accounts => {
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.relayer.should.be.eq.BN(operator)
       logs[0].args.fee.should.be.eq.BN(feeBN)
       isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(true)
@@ -285,6 +289,7 @@ contract('ERC20Mixer', accounts => {
         // public
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        relayer: operator,
         receiver,
         fee,
 
@@ -328,6 +333,7 @@ contract('ERC20Mixer', accounts => {
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.relayer.should.be.eq.BN(operator)
       logs[0].args.fee.should.be.eq.BN(feeBN)
       isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(true)

test/ETHMixer.test.js

@@ -141,6 +141,7 @@ contract('ETHMixer', accounts => {
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee,
         secret: deposit.secret,
@@ -196,6 +197,7 @@ contract('ETHMixer', accounts => {
         // public
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        relayer: operator,
         receiver,
         fee,
 
@@ -235,6 +237,7 @@ contract('ETHMixer', accounts => {
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.relayer.should.be.eq.BN(operator)
       logs[0].args.fee.should.be.eq.BN(feeBN)
       isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(true)
@@ -251,6 +254,7 @@ contract('ETHMixer', accounts => {
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee,
         secret: deposit.secret,
@@ -275,6 +279,7 @@ contract('ETHMixer', accounts => {
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee,
         secret: deposit.secret,
@@ -299,6 +304,7 @@ contract('ETHMixer', accounts => {
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee: oneEtherFee,
         secret: deposit.secret,
@@ -323,6 +329,7 @@ contract('ETHMixer', accounts => {
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         root,
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee,
         secret: deposit.secret,
@@ -350,6 +357,7 @@ contract('ETHMixer', accounts => {
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
         nullifier: deposit.nullifier,
+        relayer: operator,
         receiver,
         fee,
         secret: deposit.secret,